In the prior art, there are known silicone rubber compositions of the type wherein vinylpolysiloxane and hydrogenpolysiloxane are heat cured in the presence of a platinum catalyst through hydrosilation. These silicone rubber compositions are self-adhesive and thus useful as protective coating compositions for electronic and electric parts and as adhesive compositions for bonding electronic and electric parts to boards.
The prior art silicone rubber compositions of this type, however, are not necessarily highly adhesive to various substrates, particularly to such substrates as metals, ceramics, and plastics.
Japanese Patent Publication Nos. 13508/1978 and 5836/1982 disclose to add adhesive aids such as a hydrogenpolysiloxane having an epoxy or ester group, an ester silane compound or a hydrolyzate thereof to the silicone rubber compositions in order to increase their adhesion to various substrates.
The adhesion of the silicone rubber compositions largely depends on the temperature during curing. The silicone rubber compositions must be heat cured to the substrates at a minimum temperature of 100.degree. to 120.degree. C. even in the presence of the adhesive aids. Low temperature curing at temperatures of lower than 100.degree. C. often fails to achieve a satisfactory bond. If these silicone rubber compositions are cured at low temperatures as adhesives for electronic and electric parts, then non-bonded gaps are undesirably left between the parts and the silicone rubber composition, through which humidity and impurities will reach the parts, causing corrosion and deficient insulation to the parts.
The demand for low temperature curing is currently increasing partly as a new application and partly for an energy saving. It is thus desired to develop a silicone rubber composition capable of forming a firm bond through low-temperature curing.